The present invention relates to a transport method for the pressurised transport of carbon dioxide, a corresponding transport mixture, the use of such a transport mixture, and a corresponding transport system
The transport of carbon dioxide under pressure, for example in appropriate pressure pipes, is becoming increasingly important, inter alfa owing to new technologies.
As is known to the applicant, for example from DE 10 2009 038 444 A1 and DE 10 2009 038 445 A1, which discuss the topic in detail, carbon dioxide is used for enhanced oil recovery (EOR) within the scope of tertiary crude oil extraction. In this instance, different fluids are injected under pressure and using suitable lines into or around the relevant deposit in order to extract even crude oil fractions which are dense, viscous and/or retained in layers of rock or earth owing to a capillary effect. Gaseous carbon dioxide mixes with the crude oil to be extracted and reduces the viscosity thereof. Transport is thus facilitated.
A similar field of application of carbon dioxide lies in the extraction of methane, such as coal bed methane (CBM), i.e. methane bound adsorptively in untouched carbon deposits having a methane content of more than 90%. In this case carbon dioxide is used within the scope of enhanced CBM recovery, wherein it is likewise injected into corresponding deposits. Carbon dioxide can also be used accordingly for improved extraction of oil shales.
The term “carbon capture and storage” (CCS) encompasses technologies which are intended to contribute to reducing the amount of greenhouse-relevant carbon dioxide present in the atmosphere. The carbon dioxide accumulating in large amounts during combustion processes in fossil-fired power stations and separated accordingly has to be transported as efficiently and safely as possible to suitable storage deposits, for example saline aquifers or disused crude oil deposits. Carbon dioxide can also be converted into biomass, for example biofuels, by microalgae.
Further options for use of carbon dioxide, for example for different chemical processes for the production of fuels, methanol, urea and the like, have long been known.
Carbon dioxide is normally transported in pressure pipes above its critical point (T, P), i.e. in the ‘dense’ phase. In the dense phase carbon dioxide behaves as a compressible fluid and has a density of approximately 900 kg/m3. In order to reach the dense phase, the pressure must lie above approximately 70 bar (g). An unavoidable loss of pressure in a pressure pipe has to be compensated for by a corresponding compressor at the feed point.
As explained, for example, in the article “Dynamic simulation of a carbon dioxide transfer pipeline for analysis of normal operation and failure modes” by S. Liljemark et al., Energy Procedia 4 (2011) 3040-3047, the transport of carbon dioxide in this form poses a series of risks.
The main risk lies in the formation of a gas phase in the pipeline owing to pressure losses and/or a rise in temperature. Cavitation and/or pressure surges may thus occur and could lead to noise and vibrations. This leads to increased wear and, in extreme cases, to failure. The formation of a gas phase may occur in particular under changing conditions, such as during the filling of a pressure pipe, a change in load and/or a starting up or shutdown of a corresponding system and/or of a compressor. The damage could affect merely the pipeline itself, but could also spread to valves, flow rate measurement devices and other devices.
There is thus a need for a safer, more reliable and more economic transport of carbon dioxide, in particular in pressure pipes.